Someday, we’re going to send people to Mars, and it’s gonna be awesome.

But for now, everyone from NASA to Elon Musk is still trying to figure out the best way to do it. With today’s rockets, a one-way trip to Mars takes somewhere around seven months, but one company is developing an engine that might be able to get us there in only forty days.

It’s called the VASIMR engine, and it propels spacecraft using a jet of plasma. VASIMR stands for Variable Specific Impulse Magnetoplasma Rocket, and the idea behind it has actually been around since the 1970s. But engineers didn’t make too much progress on it until 2015, when NASA gave the Ad Astra Company a grant to develop it as part of their NextSTEP program.

It works using a kind of electric propulsion, and it’s a big step up from the other engines available right now. To get your rocket into space, you’d still need a chemical engine, which generates thrust with a reaction that releases tons of gas, like combining hydrogen and oxygen. So far, that’s the only kind of engine we have that’s powerful enough to get a heavy rocket to space.

But once you’re there, you can move it with all kinds of things, from ions to particles of light, depending on what your mission is. Right now, any spacecraft that would send people to Mars would still use a chemical engine, because we mostly have the technology figured out. But carrying all that fuel also adds a lot of weight.

So newer kinds of engines use electric propulsion, often in the form of ion thrusters, which create a beam of charged atoms, or ions, to push your spacecraft around. Ion engines are a lot more efficient than chemical engines, but they aren’t designed to handle large payloads, like a bunch of humans and all the supplies they’d need for a trip to Mars. So we mostly use ion thrusters for small satellites.

VASIMR also uses electric propulsion, but it will be way more powerful. It propels the spacecraft by creating plasma, in the form of a super hot jet of ions and electrons. Unlike other kinds of electric propulsion, it uses radio waves to heat the plasma, rather than electrodes or other electronics in ion engines.

Which among other things, makes the engine a lot more durable. To make the plasma, it starts by pumping a gas like hydrogen or argon into a tube, which is surrounded by a magnet and two couplers, a kind of device that emits radio waves. Most kinds of gas will work, which makes VASIMR really versatile, but hydrogen is a good choice if you want a lightweight, easy-to-find fuel.

Once the gas is pumped in, the first coupler strips some of the electrons off their atoms and turns the gas into plasma. At this point, it’s already very hot, around 5500 degrees Celsius, but then, the second coupler makes it even hotter. It raises the plasma to 10 million degrees Celsius, which isn’t that far from the temperature inside the Sun.

A magnetic nozzle then turns that super hot plasma into a nice, controllable jet, and it’s shot out of the end of the engine. Besides being more durable, VASIMR is great because it also has different settings, like the gears on a car, which means it can generate the right amount of thrust for different kinds of missions. So besides getting people to Mars, it could also be scaled down to send small satellites zooming around the Earth.

But most importantly for our future astronauts, VASIMR can be made big and powerful enough to move human-sized spacecraft. Ion engines just aren’t ready to do that yet, partly because many tend to rely on more mechanical parts than VASIMR, some of which aren’t designed to work on a large scale. Although engineers are working on that, too.

Still, there is one thing we need to figure out before VASIMR is ready to go: the power supply. It takes a lot of power to produce all those radio waves, especially if you want an engine strong enough to push a crew of astronauts. Solar panels can generate enough power to propel small satellites, but we’d need something a lot stronger for a full-sized spacecraft.

And our best option is probably using a small nuclear reactor. But because those have the potential to be really dangerous, we’ll want to make sure that we’re extra confident in that technology before we start using nuclear power to transport people through space. Right now, the goal for the VASIMR team is to develop an engine so it can fire for 100 consecutive hours at 100 kilowatts of power, which is 10 to 100 times more power than an ion thruster has.

To get to Mars in 40 days, you’d still need a lot more power than that, like, 2000 times more power. And that’s probably where a nuclear reactor would come in. But for now, 100 kilowatts is a good start.

Ad Astra’s plans with NASA are to have the engine ready for the 100 kilowatt goal by the summer of 2018. As of last August, they’d fired the engine for around 10 hours, so they’re making progress. Still, even after they meet that goal, VASIMR will need to go through plenty of development and tests before we use it to go anywhere.

So when the first human steps on Mars, we’ll probably have made it there with a chemical engine, since that technology is a lot more developed. But someday, our trips to Mars could be a whole lot faster. Thanks for watching this episode of SciShow Space!

If you thought getting to Mars in 40 days sounded cool, you can watch our episode on photonic propulsion, where we explain how we could someday get to Mars in only three days … at least in theory. But I wouldn’t hold your breath.